Disruption of chromosome territories in Multiple Myeloma

Abstract

Background: Multiple Myeloma (MM) is an oligoclonal cancer of plasma cells. Currently, MM is an incurable disease. MM displays altered gene expression, chromosome aberrations and altered chromosome position, which contributes to high genomic instability of MM cells. Lamin A/C is a nuclear protein that plays a critical role in the maintenance of genomic stability and nuclear architecture. Recently, our group observed that expression of lamin A/C was upregulated in MM patient samples compared to normal B-lymphocytes. Therefore, our objective was to investigate the role of lamin A/C on genome organization in MM. Methods and Results: The expression of lamin A/C in MM cell line (RPMI-8226) was confirmed by western-blot (WB) and immunofluorescence analysis. Downregulation of lamin A/C was performed using two different small interfering RNAs (siRNA), for two different regions of lamin A/C mRNA, as well as scrambled siRNA (scrRNA), used as a control. siRNA reduced the levels of lamin A/C in ∼80% in RPMI-8226 after 72-96 hours of transfection compared to scrRNA (both siRNAs). The impact of lamin A/C downregulation on chromosome territories (CT) and cell viability in MM was further analysed. The CT analysis revealed changes in CT 4,9,11,14,16,18, and 22. These chromosomes moved from the nuclear periphery to the nuclear center in RPMI 8226 after lamin A/C downregulation, compared to the scrRNA. Gene expression varies according to CT position. Analysis of siRNA lamin A/C treatment (RPMI-8226, 72 hours - quantitative PCR) shows upregulation of genes related to cell proliferation and cell survival. However, no changes in proliferation were observed. Analysis of chromatin changes using super resolution microscopy shows that downregulation of lamin A/C induces chromatin condensation (in 24 to 48 hours), followed by chromatin de-condensation (72 to 96 hours) in compared to scrRNA. Summary and Conclusion: Lamin A/C protein levels and their impact on MM cells is poorly understood. Lamin A/C plays a role in genome organization and chromosome positioning in MM. Its disruption alters chromosome positions and the expression of genes involved in MM pathogenesis. This study addresses the role of nuclear architecture in MM and highlight new insights of targeting genome organization for cancer treatment.